Circuit interrupter of the dual bore type



Sept. 10, 1968 c. w. UPTON. JR.. ETAL CIRCUIT INTERRUPTER OF THE DUAL BORE TYPE 2 Sheets-Sheet 1 Filed Aug. 24, 1967 FIG.3.

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Sept. 10, 1968' c. w. UPTON, JR, ETAL 3,

CIRCUIT INTERRUPTER OF THE DUAL BORE TYPE Filed Aug. 24, 1 967 2 Sheets-Sheet 2 FIG.6.

v-IBZ ITO FIG.5.

United States Patent 3,401,247 CIRCUIT INTERRUPTER OF THE DUAL BORE TYPE Chester W. Upton, Jr., Tratford, Calvin C. Patterson,

Bethel Park, and Frank L. Cameron, Irwin, Pa., as-

signors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Aug. 24, 1967, Ser. No. 663,127 8 Claims. (Cl. 337-221) ABSTRACT OF THE DISCLOSURE A high voltage circuit interrupter construction in which a body of arc extinguishing material is disposed inside a tubular insulating casing and includes a main bore and a smaller auxiliary bore. A larger conducting rod is disposed to extend through the main bore and a smaller auxiliary conductor is disposed to extend through the auxiliary bore and is connected at one end to the larger conducting rod for axial movement therewith. A main fusible means is connected in series with the larger conducting rod between the rod and a terminal means at one end of the casing. In order to insure initiation of arcing during any interrupting operation in the auxiliary bore, a helically coiled conductor is electrically connected between the other end of the auxiliary conductor and the terminal means with an insulated arcing terminal being connected to the terminal means to project axially away from the terminal means and to overlap the end of the auxiliary conductor to which the helically coiled conductor is connected.

Background of invention In the application of circuit interrupters, such as power fuses of the dual-bore type, at higher voltages, a problem arises in insuring that arcing during an interrupting operation is always initiated in the smaller auxiliary bore of the interrupter and that any arcing which results during the interrupting operation remains in the smaller auxiliary bore to be finally interrupted for relatively smaller fault currents which the interrupter is incapable of interrupting in the larger main bore. In order for a circuit interrupter of the type described to successfully interrupt relatively low fault currents, such as 1000 amperes or less, it is essential that the conductor in the main bore of the interrupter be permitted to move a sufficient distance to establish an adequate insulating gap and corresponding dielectric strength in the main bore prior to the time that such a relatively low fault current is finally interrupted in the auxiliary bore of the interrupter. Otherwise, the potential difference to which the main bore is subjected upon the interruption of a relatively low fault current in the auxiliary bore of an interrupter of the type described will be sufiicient to cause a restrike of the arc in the main bore in which the interrupter is not capable of interrupting relatively low fault currents of the type described. Among the reasons for the problem described found in certain known power fuse structures is the elongation of certain conducting parts associated with the main bore of the interrupter which may permit relative travel of the conductors in the main and auxiliary bores such as to produce a greater insulating gap in the auxiliary bore than in the main bore of the interrupter for relatively low fault currents. Another reason for the problem described has been found to be the premature displacement or blow out of the relatively stationary auxiliary contact provided in the auxiliary bore of an interrupter of the type described. It is therefore desirable to provide an improved high voltage circuit interrupter or power fuse construction of the dual-bore type which overcomes the problem described and which insures successful interruption of relatively low fault currents in the smaller auxiliary bore of the interrupter.

Summary of invention It is an object of this invention to provide a new and improved high voltage circuit interrupter construction.

Another object of this invention is to provide an improved means for insuring that arcing is always initiated in the smaller bore of a circuit interrupter having parallel large and small bores.

A further object of this invention is to provide an improved power fuse construction of the dual-bore type including means for insuring that relatively smaller fault currents will be interrupted in the smaller bore of the fuse.

A more specific object of this invention is to provide an improved auxiliary current path in a power fuse of the dualebore type.

Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter.

For a fully understanding of the nature and objects of the invention, reference should be had to the following detailed description, taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a side elevational view of a high voltage power fuse structure which embodies the principles of the present invention and which is shown in the normally closed operating condition;

FIG. 2 is an enlarged, longitudinal, sectional view of a fuse unit which forms part of the fuse structure shown in FIG. 1 with portions of the end fittings of the fuse unit omitted;

FIGS. 3, 4 and 5 are diagrammatic views illustrating different stages in the operation of the fuse unit shown in FIG. 2 while interrupting relatively low fault currents; and

FIGS. 6, 7 and 8 are diagrammatic views illustrating different stages in the operation of the fuse unit shown in FIG. 2 while interrupting relatively high fault currents.

Referring now to the drawings, and FIG. 1 in partic ular, the structure shown comprises a power fuse structure of the high voltage, drop-out type, the general arrangement of which is set forth more fully in copending application Ser. No. 663,020 filed Aug. 24, 1967, by R. E. Frink and C. T. Walker, which is assigned to the same assignee as the present application.

As illustrated in FIG. 1, the fuse structure 10 includes a base (not shown) formed of sheet metal and a pair of outwardly extending insulator supports 272 and 282. The upper insulator support 272 fixedly supports in position a latching assembly 250, which includes a break contact 252, as described in greater detail in the copending application just mentioned. A lower insulator support 282 supports a hinge assembly 260 which pivotally supports a fuse unit and which includes a hinge contact 262 as described in the copending application just mentioned. As illustrated in FIG. 1, the fuse unit 100 serves to electrically bridge the break contact 252 and the hinge contact 262 so that electric current will normally pass therebetween by way of terminal pads (not shown) to which an external electrical circuit may be connected.

The fuse unit 100 includes a generally tubular fuse holder 32 which is formed from a suitable weatherproof, electrically insulating material, such as a filament wound glass epoxy material or the like, and a pair of upper and lower end fittings or terminals 34 and 36, respectively, which are disposed at the opposite ends of the holder 32 and which are formed from an electrically conducting material. The upper and lower end fittings 34 and 36, respectively, are securely fastened to the opposite ends of the associated holder or tube 32 by suitable means, such as cement, and a plurality of pins which pass transversely through both the end fittings and the associated holder 32. As illustrated, the fuse unit 100 also includes a hook eye 274 which is pivotally mounted on a laterally projecting portion 34A of the upper end fitting 34 and which may be utilized for effecting opening and closing movements of the fuse unit 100 by means of a conventional hook-stick. The lower end fitting 36 includes a hinge lifting eye 284 which may be formed integrally with the lower end fitting 36 and which may be employed in conjunction with a conventional hook-stick to effect physical removal of the fuse unit 100 from the hinge assembly 260 for replacement of the fuse unit 100. The lower end fitting or terminal 36 also includes an inwardly projecting flange portion 36B against which the lower end of the holder 32 bears, as shown in FIG. 2.

The fuse unit 100 further includes a renewable or refillable unit which is mounted within the holder structure that includes the outer tube 32 and the upper and lower end fittings or terminals 34 and 36, respec tively. The renewable unit 100 includes its own supporting tube 108 which is formed from a suitable electrically insulating material having sufiicient strength to withstand the internal gas pressures and intense heat which result during an interrupting operation of the fuse unit 100, such as a filament wound glass epoxy material. A body of gas evolving material, such as boric acid, which may include a plurality of generally annular blocks 122, 124, 126 and 128, is disposed inside the tube 108 and spaced from the ends thereof. Each of the blocks 122, 124, 126 and 128 includes a relatively larger central opening and a relatively smaller opening at one side thereof, both of which extend axially through the individual blocks. When the blocks 122, 124, 126 and 128 are axially stacked in end-to-end relation as shown in FIG. 2, with the respective larger and smaller openings thereof substantially aligned, a main bore 130 is formed through the body of gas evolving material which includes said blocks and a relatively smaller auxiliary bore 192 is formed through the body of gas evolving material.

In order to prevent the travel of ionized gases between the main bore 130 and the auxiliary bore 192 during an interrupting operation of the fuse unit 100 as described in greater detail in copending application Ser. No. 663,- 018, filed Aug. 24, 1967, by C. W. Upton, Jr. and J. A. Sensue, which is assigned to the same assignee as the present application, the meeting surfaces of the blocks 122, 124, 126 and 128 are structurally joined to one another around the relatively smaller openings of said blocks which form the auxiliary bore 192 by a sealing and bonding material having a relatively high dielectric strength, such as an epoxy resin. More specifically, as explained in the copending application just mentioned, the meeting surfaces of the blocks 122, 124, 126 and 128, each includes a groove or recess which extends substantially around and is spaced from the relatively smaller opening in each of said blocks and forms with the recess in the adjacent block a combined passageway which is substantially filled with the sealing and bonding material, as indicated at 132 in FIG. 2. It is to be noted that the manner in which the blocks 122, 124, 126 and 128 are bonded to one another around the auxiliary bore 192 substantially prevents the entrance of the sealing and bonding material employed into either the auxiliary bore 192 or into the main bore 130.

In order to limit the gas pressures which result during an interrupting operation of the fuse unit 100 inside the tube 108 to a value Within the rupture strength of the tube 108, as disclosed in greater detail in copending application Ser. No. 663,126, filed Aug. 24, 1967, by C. C. Patterson, which is assigned to the same assignee as the present application, each of the blocks 126 and 128 includes a generally C-shaped recess, as indicated at 129, which entends axially from one end of each and said blocks to a point which is adjacent to and axially spaced from the other end of the respective blocks, with each of the recesses terminating peripherally short of the portion of said blocks which include the relatively smaller openings which form part of the auxiliary bore 192. Each of the blocks 126 and 128 therefore includes around a major portion of its inner periphery an integral frangible inner wall, as indicated at 126A and 128A, respectively, which is arranged to disintegrate when the fuse unit is called upon to interrupt relatively large currents and when intense heat results within the main bore and the gas pressure .within the main bore 130 exceeds a predetermined value. During such an interrupting operation, the size of the main bore through the blocks 126 and 128 is effectively increased'by the disintegration of the inner walls 126 and 128A of the blocks 126 and 128, respectively, to thereby increase the size of the gas passageway and decrease or limit the gas pressure which would otherwise result.

In order to retain the blocks 122, 124, 126 and 128 in assembled relationship with the associated tube 108, as shown in FIG. 2, the outer surfaces of said blocks may be coated with a suitable cement, such as an epoxy bonding material, prior to assembly of the blocks inside the tube 108. In addition, a generally annular retaining member or plug 189 may be disposed at the upper end of the blocks 122, 124, 126 and 128 with the major portion of the retaining member 189 extending axially inside the tube 108. The retaining member 189 may be formed or molded from a suitable, electrically insulating material having sutficient strength to assist in retaining the blocks 122, 124, 126 and 128 in assembled relationship with the tube 108 during an interrupting operation of the fuse unit 100, such as a glass polyester material. A washer 183 formed from similar material may be disposed between the retaining member 189 and the block 122 and may be employed during the preassembly and bonding of the blocks 122, 124, 126 and 128 together prior to the assembly of said blocks inside the tube 110. It is to be noted that the retaining member 189, as well as the washer 183, includes a relatively larger central opening which forms an extension of the main bore 130 and a relatively smaller opening which forms an extension of the auxiliary bore 192.

In order to assist in retaining the member 189 in assembled relation with the associated tube 108 during an internupting operation of the fuse unit 100, the outer surface of the retaining member 189 and the inner surface of the tube 108 at the upper end of the tube 108 include adjacent helical grooves which together form a passageway in which a helical wire 181 is disposed to firmly secure the retaining member 189 in assembled relation with the tube 108. The retaining member 189 may be assembled with the upper end of the tube 108 by first assembling the helical wire 181 in the helical groove around the outer surface of the retaining member 189 and then screwing the retaining member 189 into the upper end of the tube 108 to the final position shown in FIG. 2. It is to be noted that the outer surface of the retaining member 189 may also be coated with a suitable cement, such as an epoxy bonding material, to additionally secure the retaining member 189 to the tube 108.

In order to substantially prevent the escape of ionized gases from the upper end of the renewable unit 20 around the elongated conducting member 83 which extends through the main bore 130, a generally tubular member 185 is disposed in concentric or nested relation with the retaining member 189, as shown in FIG. 2, and is preferably formed from an electrically insulating material having a relatively low coefiicient of friction, such as polytetrafluoroethylene which is sold under the trademark Teflon. A shoulder portion 185A is provided at the upper end of the tubular member 185 and includes an Opening of reduced cross-section or size through which the conducting member 83 passes and which forms a substantially gas-tight seal with the conducting member 83 during an interrupting operation of the fuse unit 100 when the-conducting member 83 is actuated to move axially. The tubular member 185 also acts as a bearing to guide the axial movement of the conducting member 83. In order to prevent the tubular member 185 from being blown out of the upper end of the tube 108 during interrupting operation of the fuse unit 100, the retaining member 189 includes an inner shoulder portion against which the upper end of the tubular member .185 bears, as shown in FIG. 2. The escape of ionized gases from the upper end of the renewable unit from the auxiliary bore 192 may be adequately prevented by reducing the size of the relatively smaller opening through the retaining member 189 in which the auxiliary conductor 182 is disposed so that the cross-section of the auxiliary conductor 182 substantially fills the relatively smaller opening through the retaining member 189.

In order to further assist in retaining the blocks 122, 124, 126 and 128 in assembled relationship with the tube 108 during an interrupting operation of the fuse unit 100, a generally tubular or annular. retaining member 142 is disposed inside the tube 108 at the lower end of the blocks 122 through 128, as shown in FIG. 2, and is for-med or molded from an electrically insulating material having suflicient strength to assist in retaining the blocks 122 through 128 inside the tube 108 during such an interrupting operation such as a glass polyester material. The outer surface of the retaining member 142 is preferably coated with a suitable cement, such as an epoxy bonding material, prior to the assembly of the retaining member 142 inside the tube 108 which bonds the retaining member 142 to the inside of tube 108. The retaining member 142 includes a relatively larger opening which extends axially theretlhrough, as indicated at 142A, into which the lower end of the main bore v130 opens and which may serve as an exhaust passageway for high pressure gases which result during the operation of the fuse unit 100. The opening 142A also serves as a chamber in which the fusible means 160 is disposed. The retaining member 142 also includes a relatively smaller opening 142B, which extends axially therethrou gh, into which the lower end of the auxiliary bore 192 opens and into which the lower end of the auxiliary conductor 182 projects. The insulating wall or partition 142C around the relatively smaller opening 1428 through the retaining member 142 assists in preventing certain arc products which may result during operation of the fuse unit 100 in the relatively smaller opening 142B of the retaining member 142 from being deflected into the relatively larger opening 142A of the retaining member 142 and'impinging on parts of the fusible means 160. The retaining member 142 also includes an upwardly projecting tubular portion 142D adjacent to the relatively smaller opening 142B through the retaining member 142 with the projecting portion 142B being joined to the adjacent block 128 around a recess in the clock 128 which is adapted to receive the projecting portion 142D by a flexible bonding material, such as silicone rubber. This joint between the retaining member 142 and the block 128 around the auxiliary bore 192 serves to prevent the travel of ionized gases between the auxiliary bore 192 and the main bore 130 and between the auxiliary bore 192 and the relatively large opening 142A through the retaining member 142 during an interrupting operation of the fuse unit 100.

The elongated conducting member or rod 83 of the renewable unit 20 is normally disposed, as shown in FIG. 2, to extend through the main bore 130 with the upper end of the conducting rod 83 projecting axially beyond the upper end of the tube 108 and with the upper portion of the conducting rod 83 being externally threaded, as indicated at 83A. The conducting rod 83 is normally held in the position shown in FIG. 2 by a connection through the fusible means 160 to the generally annular or ring-shaped stationary conducting member or contact 100 which is disposed at the lower end of the casing 108 with the lower ends of the casing 108 and the retaining member 142 bearing against the top of the conducting member 100 around the central opening of the conducting member 100.

More specifically, the fusible means 160 comprises a strain element 162 and a fusible element or link 164. The upper end of the strain element 162 is secured by suitable means, such as brazing, to the lower end of the conducting rod 83, while the other end of the strain element 162 is secured by suitable means, such as brazing, to the connecting conductor or terminal 97 which is of the flat strip type. The connecting conductor 97 is secured in turn to the lower contact 100 by suitable means, such as brazing. Similarly, the upper end of the fusible element or link 164 is secure-d to the lower end of the conducting rod 83 by suitable means, such as brazing, while the lower end of the fusible element or link is secured to the lower contact 100 by suitable means, such as brazing. It is to be noted that the strain element .162 and fusible element 164 are electrically connected in parallel between the lower end of the conducting rod 83 and the lower contact 100 of the renewable unit 20.

Similarly, the auxiliary conductor 182 which is a relatively smaller cross-section or size than the conducting rod 83 normally extends through the auxiliary bore 192 with the upper end of the auxiliary conductor 182 extending axially beyond the upper end of the auxiliary bore 192 and being both mechanically and electrically connected to the upper portion of the conducting rod 83 by a transversely extending spring pin 184 which is disposed in a transversely extending recess provided at the upper end of the retaining member 189 to prevent rotation of the conducting rod 83 after assembly in the renewable unit 20. The upper end of the auxiliary conductor 182 may be formed as a loop which is assembled over the conducting spring pin 184 and retained thereon by the head 186 of the spring pin 184. The lower end of the auxiliary conductor 182 extends or projects into the relatively smaller opening 142B of the retaining member 142 and is electrically connected through a helical conducting 'wire of reduced cross-section, as indicated at 94, to the lower contact 100 of the renewable unit 20. The upper end of the helical Wire 94 which is disposed inside the relatively smaller opening 142B of the retaining member 142 is secured to the lower end of the auxiliary conductor 182 by suitable means, such as brazing, and the lower end of the helical wire 94 is secured to the lower contact 100 at the inner periphery thereof by suitable means, such as crimping or brazing.

The lower contact or conducting member 100 also includes an elongated arcing terminal which projects upwardly from the lower contact into the relatively smaller opening 142B of the retaining member 142 to axially overlap the lower end of the auxiliary conducting member 182 with the lower portion of the arcing terminal 95 being disposed adjacent to and generally parallel to the axis of the helical wire 94. The arcing terminal 95 is electrically insulated along its length by a coating or film of electrical insulation, such as an insulating enamel or heat shrinkable tubing, provided on the arcing terminal 95 to prevent the electrical shorting out of the helical wire 94. The arcing terminal 95 which is formed from an electrically conducting material may be structurally secured to the lower contact 100 at the inner periphery thereof by suitable means, such as brazing, or may be formed integrally therewith in a particular application. It is to be noted that the auxiliary current path which extends from the upper portion of the conducting rod 83 through the cross-pin 184, the auxiliary conductor 182 and the helical wire 94 to the lower contact 100 is also electrically connected in parallel with the conducting paths which include the strain element 162 and the fusible element 164.

In order to retain the lower contact 100, as well as the other parts of the renewable unit 20, in assembled relationship with the tube 108, particularly during an interrupting operation of the fuse unit 100, a generally tubular external terminal member or ferrule 110 is disposed to telescope or extend axially over the lower end of the tube 108. In order to firmly secure the external terminal member or end cap 110 to the lower end of the tube 108, the internal surface of the external terminal member 110 and the external surface of the adjacent portion of the tube 108 include aligned helical grooves which, when the parts are assembled, form a generally helical passageway in which a helical wire 173 is disposed. In the assembly of the external terminal member 110 on the lower end of the tube 108, the helical wire 173 may be first assembled in the helical groove on the lower end of the tube 108 and the external terminal member 110 may be then screwed onto the lower end of the tube 108 until the parts reach their final positions, as shown in FIG. 2.

In order to assist in retaining the stationary lower contact 100 in assembled relationship with the other parts of the renewable unit 20, the external terminal member 110 includes an inwardly projecting flange portion 110A around a central opening, as indicated at 110B, with the inwardly projecting flange portion 110A bearing against the bottom of the lower contact 100 around the periphery thereof to prevent the displacement or blow out of the lower contact 100 during an interrupting operation of the fuse unit 100. In order to form a conducting path which extends between the lower end fitting 36 and the lower contact 100 of the renewable unit 20, the external terminal member 110 also includes an external flange portion, as indicated at 110C, which bears against the inwardly projecting flange portion 36B of the lower end fitting 36. The conducting path thus formed extends from the lower contact 100 through the inwardly projecting flange portion 110A of the external terminal 110 and through the external projecting flange portion 110C to the inwardly projecting flange portion 36B of the lower end fitting 36. The area of the current transfer path between the external terminal member 110 of the renewable unit and lower end fitting 36 may also be augmented by the contact ring 120 which may be formed of electrically conducting material and which is disposed to threadedly engage the internally threaded opening at the lower end of the end fitting 36 and bear against the external terminal member 110 of the renewable unit 20, as shown in FIG. 2.

In order to actuate the axial movement of the conducting rod 83, as well as that of the auxiliary conductor 182, during an interrupting operation of the fuse unit 100 and to electrically connect the renewable or refillable unit 20 just described to the upper end fitting or terminal 34, previously mentioned, a spring and cable assembly is disposed inside the outer holder or tube 32 between the renewable unit 20 and the upper end fitting 34. The spring and cable assembly 30 includes at its lower end a generally tubular conducting member or socket 84 having an internally threaded central opening, as indicated at 84A, to receive the upper threaded end 83A of the conducting rod 83. A lower spring seat member 86 is fixedly mounted on the socket 84 for movement therewith by assembling the spring seat 86 over the outer periphery of the socket 84 with the lower end of the spring seat 86 bearing against a shoulder provided on the outer periphery of the socket 84 and with the upper end of the spring seat 86 being engaged by a plurality of portions of the socket 84 at the upper end of the socket 84 which serve to stake or secure the spring seat 86 on the socket 84. The spring and cable assembly 30 also includes an upper spring seat 74 which is slidably disposed over the lower portion 60A of a generally cylindrical conducting member 60 whose integral upper portion 603 extends axially through an opening 34B in the upper end fitting 34 and is externally threaded at the upper end thereof, as indicated at 60C. As illustrated, the generally cylindrical conducting member 60 secured to the upper end fitting 34 by an internally threaded end cap 44 which may be screwed down on the upper threaded portion 60C of the conducting member 60 until the flange portion 44A of the end cap 44 bears against the upper end fitting 34 around a flange or shoulder portion, as indicated at 34C in FIG. 2.. A helical tension spring 76 is secured at its upper endto the external-helically threaded portion of the upper spring seat 74, while the lower end of the spring 76 is secured to the externally helically threaded portionof the lower spring seat 86 to bias the conducting rod 83, as well as the auxiliary conductor 182, in a generally upward direction, as viewedin FIG. 2, away from the lower contact 100. It is important to note that the turns of the spring 76 are generally rectangular or square in cross-section to substantially prevent any overlapping of the turns of the spring 76 and the consequent damage to the spring that might otherwise result during an interrupting operation of the fuse unit 100, as explained in greater detail in copending application Ser. No. 663,021, filed Aug. 24, 1967, by C. C. Patterson, which is assigned to the same assignee as the present application.

In order to electrically connect the renewable unit 20 and more specifically the conducting rod 83 to the upper end fitting 34 both prior to and during an interrupting operation of the fuse unit 100, a plurality of helically coiled flexible cables or conductors 82 are electrically and structurally connected at the bottom end thereof to the conducing socket 84 into separate openings (not shown) provided in the socket 84 by suitable means, such as brazing or by staking, and at the upper end thereof are secured to the conducting member 60 in separate openings provided in the conducting member 60 by suitable means, such as brazing and staking. In order to increase the effective current transfer area between the conducting member 60 and the upper end fitting 34, a washer 54 formed of electrically conducting material may be disposed between the shoulder which is formed at the inner section of the upper and lower portions 60A and 60B, respectively, of the conducting member 60 and the shoulder which is formed inside the upper end flitting 34, as indicated at 34D, around the central opening 34B.

In order to facilitate the assembly of the renewable unit 20 and the associated spring and cable assembly 30 inside the outer holder 32, as will be explained hereinafter, a pair of spring pins 58 may be disposed in associated openings provided at the opposite sides of the upper portion 603 of the conducting member 60 to be positioned finally within an enlarged central opening or recess 34E in the upper end fitting 34, as shown in FIG. 2.

In order to actuate the release of the latching assembly 250 shown in FIG. 1 following an interrupting operation by the fuse unit as disclosed and claimed in copending application Ser. No. 663,021, filed Aug. 24, 1967, by C. C. Patterson, which is assigned to the same assignee as the present application, a tripping rod or member 52 is slidably disposed inside a central opening or passageway 72 which is provided in the conducting member 60 with the upper end of the tripping rod 52 being normally positioned below the top of the end cap 44, as shown in FIG. 2. The lower end of the tripping rod 52 is fixedly coupled to the upper spring seat 74 for axial movement therewith by the cross pin 56 which passes laterally through aligned transverse openings in the tripping rod 52 and the upper spring seat 74 and through a pair of elongated slots 62 provided on the opposite sides of the conducting member 60 with the cross pin 56 being normally positioned at the lower end of each of the elongated slots 62, as shown in FIG. 2. In order to permit the axial movement of the tripping rod 52 upwardly through theend cap 44 following an interrupting operation of the fuse unit 100, the top of the end cap 44 includes a central opening 46 through which thetripping rod 52 may pass upwardly to actuate the release of the latching assembly 250 shown in FIG. 1. When the latching assembly 250 is released by the movement of the tripping rod 52, the upper end of the fuse unit 100 will be actuated to rotate in a clockwise direction as viewed in FIG. 1 about the lower hinge assembly 260 to thereby provide an electrically insulating gap between the upper break contact 252 and the lower stationary hinge contact 262 by such drop out action.

In order to assemble the renewable unit and the associated spring and cable assembly into the outer holder 32, the threaded end of the conducting rod 83 is first screwed into the socket 84 at the lower end of the spring and cable assembly 30. A refill fusing tool (not shown) is then screwed into the internally threaded central opening or passageway 72 at the other end of the spring and cable assembly 30. The spring and cable assembly 30 is then inserted into the outer holder 32 with the upper end of the spring and cable assembly 30 being inserted first into the lower end of the outer holder 32, as viewed in FIG. 2, until the refill tool (not shown) passes through the central opening 34B of the upper end fitting 34. By use of the refill tool, the spring 76 is stretched and placed in tension until the cross pins 38 mounted at the sides of the conducting member 60 are drawn upwardly through a pair of radial slots (not shown) provided in the upper end fitting 34 around the central opening 34B. The upper conducting member 60 and the spring and cable assembly 30 are then rotated until the pins 58 rest on the shoulder provided at the bottom of the enlarged opening 34E in the upper end fitting 34. The end cap 44 may then be screwed down on the upper threaded portion 60C of the conducting member 60 to further stretch the spring 76 to the final position shown in FIG. 2 in which the cross pins 58 are drawn upwardly away from the shoulder in the upper end fitting 34 at the bottom of the enlarged opening 34E. 'It is to be noted that when the spring and cable assembly 30 and the renewable unit 20 are assembled inside the outer holder 32 as just described, the cross pin 56 which couples the upper spring seat 74 to the tripping rod 52 is disposed at the bottom of each of the elongated axially extending slots 62 at the opposite sides of the conducting member 60 to permit limited upward travel of the upper spring seat 74 along with the cross pin 56 and the tripping rod 52 to a final position of the tripping rod 52 in which the tripping rod 52 projects beyond the end cap axially to release the latching assembly 250, as previously mentioned. The washer 54 acts as a stop surface against which the upper end of the spring seat 74 bears to limit the upward travel of the tripping rod 52, the cross pin 56 and the spring seat 74.

In considering the operation of the fuse unit 100 it is to be noted first that the current paths which include, respectively, the strain element 162, the fusible element 164 and the helical wire 94, which is connected in series with the auxiliary conductor 182, are all electrically connected in parallel between the upper end of the conduct ing rod 83 and the lower contact 100 at the lower end of the renewable unit 20. The resistance of the current path which includes the fusible element 164 and which is calibrated to have predetermined time-current characteristics is arranged to be relatively much less than the resistance of either the path which includes the strain element 162 or the path which includes the helical wire 94 so that normally most of the current which fiows through the fuse unit 100 is carried by the fusible element 164. Although the resistance of the current path which includes the strain element 162 is relatively greater than the re sistance of the path which includes the fusible member 164, the resistance of the path which includes the strain element 162 is relatively less than that of the path which includes the helical wire 94 so that when the fusible element 164 melts or blows, most of the current which was formerly carried by the fusible element 164 will be transferred to the strain element 162. In other words, when the current which is flowing through the fuse unit 109 increases to a value which is of suflicient magnitude and duration to melt or blow the fusible element 164, most of the current which is flowing through the fuse unit 100 then transfers from the fusible element 164 to the strain element 162. When the current which is transferred to the strain element 162 after the melting of the fusible element 164 is sufiicient to melt or blow the strain element 162, the current which was previously carried by the strain element 162 is finally transferred to the current path through the auxiliary bore 192 which includes the auxiliary conductor 192 and the helical wire 94. When the strain element 162 melts or blows, the conducting rod 83 is no longer restrained from upward movement under the influence of the biasing spring 76 and the conducting rod 83 and the auxiliary conductor 182 will start to move upwardly under the influence of the spring 76 to thereby stretch the helical wire 94 which is electrically connected to the bottom of the auxiliary conductor or rod 192. It is to be noted that the stretching of the helical wire 94 permits limited travel of both the conducting rod 83 and the auxiliary conductor 182, while maintaining a continuous electrical circuit through the auxiliary bore 192 and that as long as the current path which includes the auxiliary conductor 182 and the helical wire 94 is intact, no arcing will take place in either the main bore 130 or in the auxiliary bore 192. In other words, the stretching of the helical wire 94 during the initial movement of the conducting rod 83 and the auxiliary conductor 182 following the melting or blowing of the fusible element 164 and the strain element 162 will permit the formation of an insulating gap in the main bore 130, while initially delaying the formation of an insulating gap in the auxiliary bore 192.

After the strain element 162 melts or blows as just described, and the arcing or conducting rod 83 and the auxiliary conductor 182 begin to move upwardly to thereby stretch the helical wire 94, the helical wire 94 will either fracture mechanically when stretched to its limit, as shown in FIG. 3, or the current transferred to the current path which includes the auxiliary conductor 182 and the helical wire 94 will be sufiicient to melt or blow the helical wire 94 which is of reduced cross-section compared with that of the auxiliary conductor or rod 182. After the helical wire 94 is melted or otherwise broken, an arc will be initiated between the retreating end of either the broken helical wire 94 or the auxiliary conductor 182 and the arcing terminal 95 which axially overlaps the lower end of the auxiliary conductor 182 as shown in FIG. 4 to thereby burn through the electrical insulation on the arcing terminal 95.

It is to be noted that the smaller cross-section or diameter of the helical wire 94 compared with that of the auxiliary conductor 182 controls the location at which arcing is always initiated in the auxiliary current path of the fuse unit at the lower end of the renewable unit 20 in the relatively smaller opening 142B of the retaining member 142, as shown diagrammatically in FIG. 4. In addition to the initial delay in the formation of an insulating gap in the auxiliary current path due to the presence of the helical wire 94 as previously explained, the formation of a significant insulating gap in the auxiliary current path of the fuse unit 100 is further delayed by the overlapping of the auxiliary conductor 182 by the arcing terminal 95 until the retreating free end of the helical wire 94 or the auxiliary conductor 182 passes the upper end of the arcing terminal 95 whose insulation will have burned through by this time, as shown in FIG. 5, which indicates the are between the free end of the auxiliary conductor 182 and the upper end of the arcing terminal 95 at 300. It is important to note that the insulating gap in the main bore between the separated ends of the fusible means or between the conducting rod 83 and the stationary conducting parts of the lower end of the renewal unit 20, as shown diagrammatically in FIGS. 3-5, will increase at a faster rate than the formation of an insulating gap in the auxiliary current path just described due to both the delay in'the formation of an arc in the auxiliary current path because of the presence of the helical Wire 94, as previously described, and due to the overlapping of the auxiliary conductor 182 by the arcing terminal 95 at the lower end of the auxiliary conductor 182. It is also important to note that when any abnormal current flows in the fuse unit 100 which is sufficient to melt or blow the fusible element 164 and the strain element 182 and the melting or breaking of the helical wire 94 results in the auxiliary current path, any arcing which takes place in the fuse unit will always take place initially in the auxiliary bore or auxiliary current path, as just explained. The relatively larger cross-section or size of the auxiliary conductor 182 compared with the helical wire 94 and the relatively larger cross-section or size of the arcing terminal or contact 95 provides resistance to relatively fast burn-back of the auxiliary current path when arcing is initiated as just described. In addition, the relatively rigid stationary arcing contact or terminal 95 along with the lower stationary contact 170 will remain in place during an interrupting operation to avoid the premature displacement or blow out and thus provide a positive terminal on which the arcing initiated in the auxiliary current path can impinge to keep the arc initially resulting in the auxiliary bore 192 in the path of relatively high velocity, high pressure un-ionized path flow. In order words, when the retreating end of the helical wire 94 or the auxiliary conductor 182 passes the upper end of the arcing terminal 95, the arcing which takes place initially in the auxiliary bore 192 will cause gases to be evolved from the gas evolving material around the auxiliary bore 192 which will be Lin-ionized.

When the current to be interrupted by the fuse unit is relatively low, such as 1000 amperes or less, as indicated diagrammatically in FIGS. 4 and 5, and when the gas pressure of the evolved gases in the auxiliary bore 192 increases to thereby increase the dielectric strength in the auxiliary bore 192, the insulating gap which is formed in the auxiliary bore 192 along with the increased dielectric strength will be sufiicient to interrupt the alternating current following a particular current zero in the auxiliary bore 192 during the formation of an insulating gap in the auxiliary bore 192, as just described. The insulating gap which is formed simultaneously in the main bore 130 of the fuse unit 100 will have suflicient dielectric strength considering the potential difference between the separated conducting parts in the main bore fuse unit to prevent a restrike of the arc in the main bore for such relatively low fault currents. In other words, when any fault current is interrupted by the fuse unit 100 as just described, arcing will always be initiated in the auxiliary bore 192 and for relatively small fault currents the arcing which results will be finally interrupted in the auxiliary bore. One important reason for this is that the relative dielectric strength in the main bore at the time that the arc is finally interrupted in the auxiliary bore will be relatively higher than that in the auxiliary bore to prevent a restrike or breakdown of the main bore due to the potential difference which results between the separated connecting parts in the main bore.

For relative higher fault currents, the arcing which is initiated in the fuse unit 100 will always be initiated in the auxiliary bore 192 in the manner just described. As shown diagrammatically, however, in FIG. 6, the separated ends of the conducting parts in the auxiliary current path which includes the auxiliary conductor 182 and the arcing terminal 95 will burn back to a much greater degree than for relatively low current faults and the gas pressure which builds up in the auxiliary bore 192 during the initial arcing of the fuse unit will be sufficiently high to result in a relatively higher dielectric strength in the auxiliary bore 192 compared with that in the main bore 130 between the upwardly moving conducting rod 83 and the remaining stationary conducting parts at the lower end of the fuse unit If the instantaneous potential difference between the separated ends of the conducting parts in the main bore is sufiicient when the dielectric strength of the main bore becomes relatively less than that of the auxiliary bore 130, the arc will restrike in the main bore 130, as indicated at 350 in FIG. 6, to thereby cause the evolution of un-ionized gases in the main bore 130 to thereby increase the gas pressure in the main bore 130 as well as the associated dielectric strength. In addition, as the conducting rod 83 continues to move up wardly, as indicated in FIG. 7, the conducting rod 83 may also burn back, along with the stationary conducting parts remaining in the lower end of the renewable unit 20, to thereby elongate the arc 350 and increase the un-ionized gases evolved from the gas evolving material around the main bore 130. The arc 350 will be finally interrupted, as indicated in FIG. 8, following a particular current zero in the alternating current which is being interrupted when the insulating gap in the corresponding dielectric strength in the main bore 130 is sufficient to withstand the potential difference between the separated conducting parts in the main bore 130. If the fault current which is being interrupted is of a relatively still higher magnitude, the gas pressure in the main bore 130 along the intense heat which results may be sufiicient to disintegrate the inner walls of the blocks 126 and 128 to thereby limit the gas pressure of the evolved gases to a value within the rupture strength of the tube 108, as previously explained. It is to be noted that when the arc is interrupted in the main bore 130 as just described to thereby cause the evolution of gas from the gas evolving material in the blocks 122, 124, 126 and 128 which surround the main bore 130, the upward movement of the conducting rod 130 along with the upward movement of the auxiliary conductor 182 will be accelerated additionally by the gas pressure of the evolved gases in the main bore 130 along with the force exerted on the conducting rod 83 by the bias from the spring 76.

During an interrupting operation as just described, when the conducting rod 83 is released and moved upwardly under the influence of the springs 76 or under the influence of both the spring 76 and the gas pressure of the evolved gases inside the renewable unit 20, the turns of the spring 76 which are normally held in tension will tend to collapse toward a compressed condition, but after the turns of the spring 76 partially collapse, the upper spring seat 74 will begin to slide axially on the conducting member 60 and continue to slide axially until the upper end of the spring seat 74 impacts or bears against the Washer 54 to thereby drive the tripping rod 52 in an upward direction. The tripping rod 52 will be actuated from the position shown in FIG. 2 until the upper end of the tripping rod 52 actuates the release of the latching means 250, as described in the copending application previously mentioned and in US. Patent 2,403,121 which issued July 2, 1946, to H. L. Rawlins et al. It is to be noted that the upward movement of the conducting rod 83 and the auxiliary conductor 182 will establish the insulating gaps previously described between the separated ends of the conducting parts inside the renewable unit 20 following an interrupting operation. As previously mentioned, the fuse unit 100 would be actuated by the release of the latching means 250 to rotate in a clockwise direction about the lower hinge assembly 260 in a drop-out movement to establish an additional insulating gap between the break contact 252 and the lower stationary hinge contact 262 of the fuse structure 10.

It is to be noted that during an interrupting operation of the fuse unit 100 for either relatively low fault currents or relatively high currents as previously described, the electrically insulating wall or barrier 1420 provided in the retaining member 142 substantially prevents the deflection or impingement of arc products from the arcing which is initiated in the auxiliary current path for all magnitudes of currents from impinging on the separated conducting parts in the main bore or relatively larger 13 opening 142A of the retaining member 142 and possibly causing an undesirable restrike of the arc in the main current path of the fuse unit 100.

It is to be understood that the teachings of the applicants invention may be applied to power fuses for high voltage applications which are the non drop-out type as disclosed in copending application Ser. No. 663,021, filed Aug. 24, 1967, by C. C. Patterson, which is assigned to the same assignee as the present application. It is also to be understood that the teachings of the applicants invention may be applied to power fuses for high voltage ap plications which include a tubular conducting member or shield of the type disclosed in copending application Ser. No. 663,029, filed Aug. 24, 1967, by F. L. Cameron, which is also assigned to the same assignee as the present application.

The apparatus embodying the teachings of this invention has several advantages. For example, arcing is always initiated in the auxiliary current path of the fuse structure disclosed due to the delay in the formation of a significant insulating gap in the auxiliary current path which is due both to the stretching of the helical wire 94, as disclosed, and also to the overlapping of the lower end of the auxiliary conductor 182 by the elongated arcing terminal 95, as previously described. In addition, the disclosed construction assures a positive stationary terminal at the lower end of the auxiliary current path in a fuse unit as disclosed which is prevented from being displaced or blown out during an interrupting operation to improperly cause the dielectric strength of the auxiliary current path to exceed that of the main current path when the fuse unit is called upon to interrupt relatively low fault currents. A further advantage of the disclosed construction-is that a fuse structure as disclosed including an auxiliary current path as disclosed permits a relatively large exhaust gas passageway at the lower end of the fuse structure to permit the exhaust of relatively high pressure gases which may be evolved or resulting during an interrupting operation of the fuse unit.

Since numerous changes may be made in the above described apparatus and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all the matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

We claim:

1. A circuit interrupter comprising a tubular insulating casing, a body of arc extinguishing material disposed inside of and spaced from the ends of the casing and including a larger opening extending axially therethrough and a smaller opening extending axially therethrough, terminal means disposed adjacent to at least one end of the casing, an elongated, larger conducting member disposed to extend axially through the larger opening, fusible means disposed inside the casing and connecting between one end of the elongated conducting member and the terminal means, an elongated, smaller conducting member disposed to extend axially through the smaller opening and secured at one end to the larger conducting member adjacent to the other end of the larger conducting member for axial movement therewith, a helically coiled conducting member of relatively smaller cross-section than that of the smaller elongated conducting member disposed inside the casing and connected between the other end of the smaller elongated, conducting member and the terminal means, and an electrically insulated arcing terminal connected to said terminal means and disposed adjacent to the helically coiled conducting member to project axially away from the terminal means and to axially overlap the other end of the smaller, elongated conducting member.

2. The combination as claimed in claim 1 wherein the fusible means including a strain element and a main fusible element electrically connected in parallel between the larger conducting member and the terminal means.

3. The combination as claimed in claim 1 wherein a generally tubular, electrically insulating member is disposed inside the casing between the body of arc extinguishing material and the terminal means, said insulating member including a larger opening extending axially therethrough in which the fusible means is disposed and a smaller opening therethrough in which the helically coiled conducting member and at least a portion of the arcing terminal are disposed.

4. The combination as claimed in claim 1 wherein an electrically insulating partition is disposed inside the casing between the fusible means and both the helically coiled conducting member and the arcing member.

5. The combination as claimed in claim 1 wherein means is connected to the larger conducting member adjacent to the end away from the terminal means for actuating the larger conducting member and the smaller conducting member axially away from the terminal means when the fusible means blows.

6. The combination as claimed in claim 5 wherein an electrically insulating partition is disposed inside the casing between the fusible means and both the helically coiled conducting member and the arcing terminal.

7. The combination as claimed in claim 5 wherein the fusible means includes a separate strain element which normally restrains the axial movement of the larger and smaller conducting means away from the terminal means.

8. The combination as claimed in claim 5 wherein a generally tubular, electrically insulating member is disposed inside the casing between the body of arc extinguishing material and the terminal means, said insulating member including a larger opening extending axially therethrough in which the fusible means is disposed and a smaller opening extending axially therethrough in which the helically coiled conducting member and at least a portion of the arcing terminal are disposed.

References Cited UNITED STATES PATENTS 2,183,728 12/1939 Triplett 200-420 XR 2,319,277 5/ 1943 Triplett 200-420 2,961,514 11/1960 Lindell 200 2,976,381 3/1961 Lindell 200-120 BERNARD A. GILHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner. 

